A conflict is no longer quite so unthinkable. Here's how the U.S. would fight such a war--and the huge price it would have to pay to win it

The first message was routine enough: a "Prepare to Deploy" order sent through naval communications channels to a submarine, an Aegis-class cruiser, two minesweepers and two mine hunters. The orders didn't actually command the ships out of port; they just said to be ready to move by Oct. 1. But inside the Navy those messages generated more buzz than usual last week when a second request, from the Chief of Naval Operations (CNO), asked for fresh eyes on long-standing U.S. plans to blockade two Iranian oil ports on the Persian Gulf. The CNO had asked for a rundown on how a...